Maidenhair Spleen wort 73 



Asplenium trichomanes Linnaeus, Species Plantarum, 1080. 1753. 



YOUNG plants of Asplenium trichomanes are apt to be con- 

 fused with those of A . platyneuron, but can be easily distinguished 

 by the dark petioles of the very young leaves.* The petiole is 

 partly or entirely green in the young plant's first leaf, but becomes 

 almost at once, in succeeding leaves, dark and lustrous, shading 

 from stramineous-brown to dark purplish-brown. 



Narrow membranous wings on the sides of the petiole, and 

 of the rachis if there is one, are visible from a very early stage of 

 leaf-development, if not from the first. At first the leaf-blade is 

 roundish-spatulate, and contains a simple vein. It then becomes 

 spatulate and obscurely notched at apex, next obcordate, and 

 then cuneate-bilobed ; and the vein sends out two branches at 

 apex, each occupying one of the lobes. The leaf-blade then be- 

 comes slightly more complex, lobed, and crenate, and its primary 

 vein (midvein) develops somewhat beyond the two first primary 

 branches. 



The parts of the leaf-blade that contain these two basal primary 

 branches then separate from the upper part of the leaf-blade 

 sufficiently to form two pinnae, while the part of the leaf-blade 

 remaining above them that contains the section of the leaf's 

 primary midvein between the latter 's first (basal) and second 

 pair of primary branches becomes elongate and attenuate, form- 

 ing a rachis, over which the dark color of the leaf's petiole spreads 

 quickly. Additional pairs of pinnae are added successively to the 

 leaf in a similar way; by parts of the leaf containing the pair of 

 primary branches of the leaf's primary midvein, next above the 

 last pair of pinnae previously formed, separating from the upper 

 part of the leaf sufficiently to form a pair of pinnae, while the part 



* See page 71. 



